Solid sealant with environmentally preferable corrosion resistance

Abstract

The faying surface of one or of both of a pair of substrates is provided with a layer of solid polyurethane sealant which is adherent to at least one of the respective surfaces. The substrates are additionally fastened together so that the faying surfaces compress the polyurethane sealant between them to form a fluid seal across the entire spacing between the two surfaces, and between the polyurethane sealant and the faying surfaces themselves.

I claim:  
     
       1. A sealant for forming a fluid seal between the faying surface of two metallic substrates that are compressively and mechanically joined together, said sealant being liquid in its pre-cured condition and a dry solid in its cured condition, the transition from pre-cured to cured condition occurring at room temperature with a cure time not less than about 10 minutes and not more than about 16 hours, said sealant when cured having a Shore A hardness between about 30 and about 70, being impermeable and resistant to chemical attack by air, water, common solvents and petroleum fuels, resistant to compressive cold flow but deformable to conform to an abutting one of said surfaces or with a layer of similar sealant on the other of said surfaces, and flexible and resistant to a temperature range between about −65 degrees F and about 250 degrees F, said sealant comprising a cured copolymer of an isocyanate and a polyol, both the isocyanate and polyol having at least two functionalities, and the isocyanate and polyol when mixed before curing containing a dibutyl tin dilaurate catalyst in an amount respective to an intended cure rate, said sealant including a metal borate corrosion resistance component. 
     
     
       2. A sealant according to claim  1  in which the isocyanate and polyol when mixed before curing contains said metal borate. 
     
     
       3. A sealant according to claim  2  in which the metal borate is zinc borate in amounts by weight between about 3% and about 30% of the sealant. 
     
     
       4. A sealant according to claim  3  in which the zinc borate is in amounts between about 6% and about 12% by weight of sealant. 
     
     
       5. A structural assembly comprising a pair of metallic substrates each having a faying surface, said faying surfaces facing toward one another; 
       a layer of sealant between said faying surfaces and adherent to at least one of them; and  
       fasteners compressively holding said surfaces against said sealant layer to form a seal between said surfaces;  
       said sealant comprising a sealant for forming said seal between said faying surfaces said sealant being liquid in its pre-cured condition and a dry solid in its cured condition, the transition from pre-cured to cured condition occurring at room temperature with a cure time not less than about 10 minutes and not more than about 16 hours, said sealant when cured having a Shore A hardness between about 30 and about 70, being impermeable and resistant to chemical attack by air, water, common solvents and petroleum fuels, resistant to compressive cold flow but deformable to conform to an abutting one of said surfaces or with a layer of similar sealant on the other of said surfaces, flexible and resistant to a temperature range between about −65 degrees F and about 250 degrees F, said sealant comprising a cured copolymer of an isocyanate and a polyol, wherein both the isocyanate and polyol have at least two functionalities, and the isocyanate and polyol when mixed before curing contain a dibutyl tin dilaurate catalyst in an amount respective to an intended cure rate, said sealant including a metal borate corrosion resistance component.  
     
     
       6. A structural assembly according to claim  5  in which the isocyanate and polyol when mixed before curing contains said metal borate. 
     
     
       7. A structural assembly according to claim  6  in which the metal is zinc borate in amounts by weight between about 3% and about 30% of the sealant. 
     
     
       8. A structural assembly according to claim  6  in which the zinc borate is in amounts between about 6% and about 12% of the sealant.